Week 8: Mass Wasting in the US

 

This week we are discussing 'mass wasting' events...aka, landslides, mudslides, rockslides, etc.

These hazards are connected to others like earthquakes or flooding or wildfires.... although mass wasting events do not need any triggers (just gravity!). As an example, a 7.3 magnitude earthquake hit NE Japan and provoked several landslides and rockslides (image below).

Landslides in the United States cause approximately $3.5 billion in damage and kill between 25-50 people annually. The US Landslide inventory map below shows these hazards widespread within the country.

The largest landslide in modern U.S. history (in terms of volume) was most likely one that occurred in 2013 in Bingham Canyon outside of Salt Lake City, Utah. It had a slide mass of 55 million cubic meters (compared to an estimated 10 million cubic meters during the Oso event in 2014).

Landslides impact California’s terrain often. These are generally related to precipitation patterns, in particular if there has been previous months of drought conditions. In January 2019, Pacific storms brought a lot of rainfall to the state. The heavy rain forced residents to evacuate from wildfire-ravaged areas. The “high risk” areas for mudslides are so because they are adjacent to steep slopes or are located at the base of drainage areas. Recent examples are the ‘Woolsey’ and the ‘Hill’ fire burn areas, which will be subject to high volume of mud and debris flow moving forward. 

If you want to know more about these hazards, the USGS page has great information on how to identify landslides and what to do if one happens. If you want to know if you are living in a risk area, you can access maps like the USGS below that shows the Emergency Assessment of Post-Fire Debris-Flow Hazards.

Stay informed and safe-